It is common in certain heat exchanger constructions, such as radiators, to provide a header/tank assembly wherein an elastomeric seal or gasket is located in a receiving groove, channel or well in the header plate and then compressed between the header plate and the tank to seal the joint therebetween. One problem associated with such constructions is the failure mode sometimes referred to as gasket-out-of-well (GOW), wherein the gasket is not located properly in its receiving well and ultimately fails to seal the associated joint, thereby resulting in a leak. Often this condition occurs because the gasket rides up on an inner wall of the receiving well due to a short gasket condition and is visually undetectable in the assembled state of the tank/header assembly. There are a number of approaches to overcome this problem. One approach involves the use of a suitable gasket lubricant or seal compound to temporarily “glue” the gasket in its proper location during assembly. However, this approach is often not reliable. Another approach, shown in German Patent No. DE 42 43 495 A1, is to provide a locating tab on the gasket that is received in a slot formed in a side wall of the gasket well. While this approach may prove successful, there is always room for improvement.